Conventionally, as a method for producing 2-(alkyl)cycloalkenone from 2-(1-hydroxyalkyl)cycloalkanone, for example, JP-A 56-147740 discloses a method in which after dehydrating an aldol condensed compound with oxalic acid, isomerization reaction is allowed using hydrogen bromide and hydrochloric acid, or a method in which dehydration reaction and subsequent isomerization reaction are simultaneously conducted with the use of hydrogen bromide and hydrogen chloride. When using strong acids such as hydrogen bromide and hydrogen chloride, the reaction proceeds to isomerization reaction as well as dehydration reaction. However, since 2-(1-hydroxyalkyl)cycloalkanone which is a raw material and 2-(alkyl)cycloalkenone which is a product polymerize and decompose, decrease in yield is inevitable.
Additionally, in comparison with the reaction wherein the above dehydration reaction and isomerization reaction simultaneously take place, a two-step method in which isomerization reaction takes place after dehydration reaction using a weak acid such as oxalic acid sometimes causes deterioration in yield due to polymerization and decomposition of 2-(alkyl)cycloalkenone when the dehydration reaction is forced to proceed to a high conversion ratio.
On the other hand, JP-A 2001-328965 discloses a method of simultaneously conducting dehydration reaction and isomerization reaction by acting a catalyst containing amine and hydrogen halide on 2-(1-hydroxyalkyl)cycloalkanone. However, the temperature that allows efficient isomerization reaction is in the range of 80 to 200° C. in industrial production.